Relation of Linux to UNIX

In about 2-3 paragraphs to help me better understand
What is the relation of Linux to UNIX?

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"What is the relation of Linux to UNIX?"
- "This is an extremely complicated question that confuses many people new to the *nix world. Historically, Unix was developed at Bell Labs in the late 60s, though it didn't really come into its own until development through the 70s. Originally, it was just an experiment on the part of the authors - Dennis Ritchie, Ken Thompson, Brian Kernighan, et al - that attained a sort of acceptance at Bell and excited the academic community.

As Bell was originally forbidden to sell operating systems due to monopoly issues, it was originally distributed in the form of source code on tapes and, the story goes, often with a note saying "Love, Ken [Thompson]". So it was proprietary in the sense that Bell owned it, but open source in the sense that people could see and modify the code. Over the course of time, it became more and more popular (and thus potentially more and more profitable). When Bell (AT&T) was broken up, the legal obstruction to selling Unix was removed. Several different companies developed their own versions of Unix which became increasingly less interoperable and further redistribution of the source code (or any distribution of new code) was forbidden. ...